1. Field of the Invention
The present invention relates to a packaging apparatus of a terahertz device, and more particularly, to a packaging apparatus of a terahertz device that is realized as one independent apparatus to easily perform a characteristic test and keep and maintain the terahertz device.
This work was supported by the IT R&D program of MIC/IITA [2006-S-005-02, Development of THz-wave oscillation/modulation/detection module and signal sources technology].
2. Description of the Related Art
Terahertz (THz) wave is electromagnetic wave that is in the frequency range from 0.1 to 1 THz between microwave and infrared rays. The THz wave is in the region between existing radio wave and a light region. The region corresponds to a technical limitation of radio wave and optical technology and has been known as one of the most inaccessible regions of the electromagnetic spectrum.
However, high-power THz sources appeared with the widespread use of a femtosecond laser and the development of material technology and nano-scale processing technology, and a significant development in this field has been made.
Therefore, THz wave has attracted worldwide attention in that the THz wave will be used in various application fields in the future because of characteristics of the THz wave.
Spectroscopy and imaging techniques using inherent characteristics of the THz wave has been growing as an attractive research field as they have attracted attention from a high-tech industry and various kinds of higher-value added services, for example, a new substance, a medical service, a biotechnology, security, national defense, universe, and communication.
Further, from the fact that developed countries include techniques related to the THz wave as one of the most important future technologies, it can be expected that the THz wave has a large-scale application and a strong ripple effect.
THz wave can be divided into continuous type and pulsed type according to a generation method thereof. When THz wave is generated by a femtosecond laser, the generated THz wave belongs to pulsed THz wave type. Since the THz wave is pulse type having short durations of picoseconds or less, if the THz wave is converted into the frequency domain, ultra-wide band electromagnetic wave in the frequency range of hundreds of GHz to tens of THz can be obtained.
In general, the pulsed THz wave is generated by using a photoconductive antenna (PCA), optical rectification (OR), and a surface-field of semiconductor.
FIG. 1 is a view illustrating the concept of generating THz wave by using a photoconductive antenna.
As shown in FIG. 1, a photoconductive antenna is formed in such a way that a photoconductive thin film 11 is deposited on a semi-insulator GaAs device substrate 10 and a metal parallel transmission line (also used as an electrode) 12 having a protrusion at the center thereof is formed thereon.
Further, the protrusion formed at the center of the metal parallel transmission line 12 serves as a small dipole antenna.
While a bias voltage Vb is applied to the metal parallel transmission line 12, if the metal parallel transmission line 12 is intermittently excited by using laser pulse light fs having a time width of 100 femtoseconds or less, carriers (electrons and holes) are generated by optical absorption, a current instantaneously flows through the metal parallel transmission line 12, and THz wave (dipole radiation) in proportion to a time differentiation value of the current is generated.
That is,
  E  ∝            ∂              i        ⁡                  (          t          )                            ∂      t        ∝                    ∂        2            ⁢              P        ⁡                  (          t          )                                    ∂        2            ⁢      t      is obtained.
Here, E is a radiation electric field at a long distance (direction), i(t) is a photoconductive current, and P(t) is polarization.
THz wave is strongly radiated from the surface of a substrate having a high permittivity. The radiated THz wave has a pulse width of 1 ps or less. When light excitation is performed by using a general-purpose laser pulse of 30 fs or more, wide spectrum extending from 0 to few THz is obtained by fourier transform.
Since the small dipole antenna has a gap width of 5 μm, it is sufficiently smaller than a wavelength of the THz wave radiated at hundreds of μm. Therefore, when the current excited by optical pulse flows, it is considered that carriers move with the same phase as one group. Therefore, the THz wave being generated corresponds to coherent radiation.
As described above, the THz wave is radiated from the surface of the semiconductor. Here, the THz wave is radiated when a current is instantaneously generated by a built-in electric field existing in the semiconductor surface and when excited charges move by diffusion, which varies semiconductor materials and excitation conditions.
However, as described above, in order that the electromagnetic wave is radiated from the semiconductor surface, a high-precision alignment technology needs to be involved. This is the fundamental reason why the present invention is required.
FIG. 2 is a front view illustrating a terahertz device using a general photoconductive antenna.
Referring to FIG. 2, the terahertz device includes a photoconductive antenna-type metal pattern 21 that is formed by patterning a GA/AS device substrate and electrode pads 22 that are formed at both ends of the metal pattern 21.
As described above, the terahertz device, shown in FIG. 2, receives laser pulse light fs in which pulses of light are 100 femtoseconds long or less, generates THz wave, and radiates the THz wave to the outside.
However, since the terahertz device having the above configuration cannot be packaged as a complete device, in order to test characteristics of the device, the terahertz device needs to be electrically or mechanically connected to a test system by using a conductive adhesive or performing indium adhesion. That is, an electric line that is connected between a power supply that applies a high electric field and a contactor of the test system needs to be directly connected to the metal pattern 21 of the terahertz device.
Therefore, it is very difficult and complex to test the characteristics of the terahertz device.
Further, after the test is completed, since signal lines connected by using the conductive adhesive and indium adhesion need to be removed, the alignment of the device is skewed and contaminated. Therefore, the terahertz device cannot be reused.
Further, as described above, since the terahertz device cannot be packaged, the terahertz device is very susceptible to damage or contamination by an external environment. Therefore, it is very difficult to carry or keep the terahertz device.